Electrohydraulic flow control apparatus



Nova 16, 1965 c. E. ADAMS 3,217,741

ELECTROHYDRAULIC FLOW CONTROL APPARATUS Original Filed April 4, 1961INVENTOR. CECIL E. ADAMS States This invention relates to apparatus foradjustably controlling the rate of flow of hydraulic fluid underpressure. More particularly, the invention relates to electricallycontrollable apparatus for adjustably regulating the rate of flow ofhydraulic fluid under variable pressure conditions.

This application is a division of my co-pending application Serial No.100,753, filed April 4, 1961, now Patent No. 3,159,178, issued December1, 1964.

Devices for regulating the flow of hydraulic fluid have utility for awide variety of purposes. For example, such devices are commonlyemployed to permit only a fixed number of gallons of fluid per minute toflow to a hydraulic motor, thereby maintaining the speed of rotation ofthe motor at a fixed number of revolutions per minute. As anotherexample, it is often desirable to admit fluid at a constant flow rate tothe cylinder of a hydraulic ram so that the ram will advance at constantspeed regardless of variations it may encounter in the resistancepresented to it by a workpiece.

While there have heretofore been available flow control devices whichpermit adjustment or change in the volume of flow which they permit topass in unit time, it has usually been necessary to make suchadjustments manually, as by loosening a lock nut, changing the relativeposition of an orifice-forming element, and then retightening the nut.For obvious reasons, it has been difiicult to make such adjustmentsremotely. Moreover, it has been difficult quickly to set previous flowcontrol devices to maintain the flow rate at a precise preselectednumerical value. For example, if it is desired, say, to maintain a flowrate of 4 gallons per minute to a hydraulic motor, the flow controlapparatus must usually be set so that the flow rate will approximate thedesired value. With the apparatus thus set, the actual flow must then bemeasured and the setting of the apparatus inched to a betterapproximation of the desired rate. That this type of adjustment has beendifficult to eflect remotely can also be appreciated.

In contrast to such past devices, this invention is directed to flowcontrol apparatus which is electrically controllable and by which thevolume of fluid supplied to a work load may be remotely adjusted to, andautomatically maintained at, a preselected value with very high accuracyand with very low variation.

Broadly speaking, the flow control apparatus of this invention includesstructure forming a main orifice, structure forming a pilot or trimmerorifice, fluid passageways through which fluid under pressure issupplied to the respective inlets of the main and pilot orificestructures, and pressure differentially operated means whereby the pilotor trimmer orifice structure is rendered effective to control the totalflow of fluid through the flow control apparatus.

More specifically the invention comprises a main flow orifice assembly,a pressure regulator assembly, and a trimmer or pilot valve. The mainflow orifice assembly includes a body having an inlet port and an outletport and structure forming an adjustable or variable orifice betweenthose ports the area of which can be varied. The pressure regulatorassembly maintains a constant atent ice pressure differential orpressure drop between the pressure of fluid at the inlet and outletports of the main flow orifice assembly. The trimmer or pilot valveincludes a body having a bore, an inlet port and an outlet port, amovable valve member for establishing a pressure drop between the inletand outlet ports, and an electromechanical transducer for actuating thevalve member which delivers a substantially constant force for a givenelectrical input thereto in a direction tending to close the pilotvalve. A fluid passageway communicates between the inlet port of themain flow orifice assembly and the inlet port of the trimmer or pilotvalve, and a second passageway communicates between the outlet port ofthe main orifice assembly and the outlet port of the trimmer, one ofthese two fluid passageways including a flow restrictor for throttlingflow through the trimmer.

These and other aspects of the invention may best be described byreference to the accompanying drawings, in which:

FIGURE 1 isa schematic diagram of a hydraulic system in accordance witha preferred form of the invention, incorporating a two-port flow controlapparatus in a bleed-off circuit for very accurately regulating the flowto a fluid motor, including a cross-sectional view of anelectrohydraulic trimmer, electric circuitry for controlling the settingof the trimmer, and a cross-sectional View of a flow metering assembly;and

FIGURE 2 is a horizontal section through the flow metering assembly online 22 of FIGURE 1.

In FIGURE 1 of the drawings there is shown a system in accordance withthe invention for supplying hydraulic fluid under pressure to a fluidmotor whereby the motor is moved or turned at a very accuratelycontrolled rate. The operation of this system is controlled by anelectrical input supplied to it. It can be set, by closing anappropriate switch, to provide any of a number of preselected operatingranges over each of which the rate of movement can be either graduallyvaried or set at any value in the range simply by adjusting a variableresistor. In accordance with this system, an adjustable orifice ispre-adjusted to establish a flow approximating the flow which isactually desire-d, while a trimmer valve connected in parallel with thevariable orifice enables the total flow to be very closely regulated andmaintained electrically to within 1% or less of the actual valuedesired.

Broadly speaking, the system of FIGURE 1 includes a source 11) of fluidunder pressure, a work load 11 which for purposes of illustration istaken to be a fluid motor, a main flow metering assembly designated by183, a trimmer or pilot valve 13, and an electric circuit 14 foroperating and controlling the pilot valve 13.

Referring to the figure in detail, the source of fluid pressure 10 isconventional and may comprise an electric motor 16 driving a hydraulicpump 17. The pump receives hydraulic fluid from a tank 18 through aconduit 20, and discharges fluid under pressure into a conduit 21. Thisconduit 21 is connected to tank 18 through a relief valve 22 and aconduit 23. These elements 16-- 23 will be understood to represent aconventional source of fluid under pressure by which the work load 11 isoperated.

Conduit 24 is connected to fluid motor 11 through conduit 181 The lowpressure side of fluid motor 11 is connected to tank 18 through conduit28. A bleed-01f or bypass conduit 181 is connected at one end to conduit24 and at the other end to the inlet port 182 of the main flow meteringassembly 183. The main flow metering assembly 183 has a tank port 184, ahigh pressure pilot inlet port 185 and a low pressure pilot port 186which communicates with tank port 184.

Thus, the main flow metering assembly and the trimmer valve areconnected in parallel with the fluid motor in a bleed-off or by-passcircuit between the high pressure conduit and the tank. The flow to thefluid motor is equal to the flow from the pressure source minus thatwhich is passed by the main flow metering assembly and the trimmer; bymetering the flow which is by-passed around the fluid motor, the mainflow metering assembly and trimmer thereby determine the total flow tothe fluid motor. Those skilled in the art will recognize that thissystem is of the two-port, meter-out type.

The main flow metering assembly, as will be explained is preset topermit flow of a constant fixed amount to pass. Since in practice it isdiflicult to set the main flow metering assembly to provide exactly thebypass flow desired, the trimmer or pilot valve is employed to bring thetotal by-pass flow very accurately to the desired value and to maintainit at that value within narrow limits regardless of pressurefluctuations. For that reason the trimmer can be thought of as asecondary flow metering assembly which operates in conjunction with themain flow metering assembly 183.

Main flow metering assembly 183 includes a body 187 in the form of ablock which may in practice be integral with block 97 upon which thepilot valve 13 is mounted, although the two are shown separately in thedrawing for clarity. The body 187 is provided with two through bores 183and 189, the axes of which extend at right angles to each other and arespaced apart. Bore 188 contains elements which cooperate to formpressure compensating or regulating means, while bore 189 containselements which cooperate to form a variable orifice by which the rate offlow of fluid is directly controlled or metered.

The elements contained within bore 188 include a cylindrical element 36having spaced circumferential grooves 37, 38, and 39 formed therein,which is inserted into one of the open ends of bore 188 and is retainedtherein by a snap ring 41. The cylinder 36 is sealed to the bore by anO-ring contained within groove 37 which is adjacent snap ring 41.Cylindrical 36 also includes a central axially extending bore 42 whichextends upwardly toward but not through its upper end which is connectedto grooves 38 and 39 by passages or ports 43 and 44 respectively. Groove38 communicates with inlet port 182, and groove 39 communicates withport 185.

A compound piston element 46 is also contained within bore 183 andincludes a piston head 47 of diameter equal to that of bore 188 and asmall diameter shank 4% which extends to and reciprocates within bore 42of cylinder 36. This shank 48 is provided with a circumferential groove59 flanked by a pair of lands 51 and 52. Land 51 functions merely as aguide or bearing for the compound piston 46 and never closes port 43.Land 52 cooperates with port 44 to form a valve for controlling the flowof fluid through port 44 in accordance with the vertical position of thesharp upper peripheral edge or" the land which is adjacent groove 59.The compound piston 46 is provided with a vertical bore 53 which extendsdownwardly from its upper end and communicates through a lateraldrilling 191 with groove 59.

The piston 46 is urged upwardly to the position shown in FIGURE 1 by aspring 55 which abuts the piston head 47 and a block 56. Spring 55 is alow rate spring; that is, the force it supplies when compressed isrelatively independent of the degree of compression it has undergone.The block 56 is inserted into the other open end of bore 183, sealed byan O-ring 57, and is retained in the bore by a snap ring 58. The block56 forms an abutment which limits the downward movement of the piston 46in bore 188. The chamber formed in the bore between the upper face ofthe piston head 47 and the adjacent end of cylindrical element 36 isconnected with groove 39 by a passage 69 formed in the cylindricalelement and extending from port 44 to the bottom of element 36.

The elements in bore 139 which cooperate to form the adjustable orificeinclude a sleeve 192 which has a close fit with the bore. This sleeve192 is provided with two circumferential grooves 193 and 194 (see FIGURE2) which are separated by a land 195. The upper end of sleeve 192 issealed by an O-ring 196 contained in a groove formed in the sleeve.Another O-ring 197 lies in a groove formed in body 187 around the lowerend of the sleeve 192 and is held therein by suitable means not shown.

Groove 19 1 in sleeve 192 communicates with the axial bore 199 of thesleeve by ports 193 formed through the wall of the sleeve, and groove193 is connected to bore 199 by a slot 293 having sharp edges where itjoins bore 199. Bore 199 is cylindrical and receives a valve element 264which is adjustable both longitudinally and rotationally in the bore.This element 294 comprises two cylindrical portions 205 and 296 ofdifferent diameters sep arated by a shoulder. The larger diameterportion 296 fits closely but movably in the interior 199 of sleeve 192;to form a substantially fluid tight fit therein and is pro vided with acircumferential groove 297 adjacent the shoulder in which there is anO-ring for preventing the loss of fluid along its surface toward theshoulder. As can best be seen from FIGURE 2, the lower portion 296 ofvalve element 294- is also provided with a circumferentially extendinggroove 2% which communicates with bore 199 in sleeve 192. This groove208 is intersected by a slot 299 extending at right angles to the axisof the valve element 294. The depth of this slot 299 is such that thebottom of the slot lies substantially on the axis of the valve element294, and the axial dimension of the slot is greater than that of groove298. The lower most side wall of slot 299 is coplanar with the lowermostside wall of groove 203, while the uppermost side wall of slot 299 liesin a plane above the plane of the upper most side wall of groove 2118,defining a solid semi-circular portion where it joins the walls of slot299. This slot 2299, upon rotational or axial adjustment of valveelement 2%, serves to adjust the area of the adjustable orifice formedby it and rectangular slot 203. Means for adjusting and securing theposition of slot 299 with respect to slot 293 are not shown in thedrawing but may, for example, comprise a lock nut threaded on the upperportion 295 of valve element 294 which is engageable with body 187.

By reference to FIGURE 2, it can be seen that when the valve element 294is moved upwardly in bore 189, the effective width of slot 293 will bechanged, and when valve element 294- is rotated, one or the other endsof slot 299 and the valve element will function to adjust effectivelength of slot 203. The inlet or trimmer valve 13 employed in thissystem is mounted on block 97 which includes an inlet passageway 98connected to high pressure pilot port 185 of the main flow meteringassembly 183. Block 97 also contains an outlet passageway 104 which isconnected to the low pressure pilot port 186.

The pilot valve 13 is housed in a body comprised of two elements and 96which are connected by screws not shown. The lower body element 96 isprovided with a flat bottom surface for mounting atop block 97 which, asexplained, can in practice be contiguous with the main flow meteringassembly 183. An O-ring 1111 in a groove in the lower surface of bodyelement 96 forms a seal with the top surface of block 97. inletpassageway 98 extends from port of the flow metering assembly 183through a restricted orifice 99 to the upper surface of block 97 whereit forms an inlet port 1%. Outlet passageway 1% opens on the top surfaceof block 97 at a position spaced from inlet port 191).

The lower body element 96 of the pilot valve is provided with a steppedvertical bore 105 which is axially aligned with port 199 and which isenlarged at its lower end to communicate with the outlet passageway 194.This bore 195 is divided into two chambers, one a wet chamher 106 andthe other a dry chamber 107, by a seal and guide assembly 108 and adiaphragm 109 in the form of a flexible boot. Bore 105 is joined belowthis boot 109 by a horizontally extending bore 111 which is partiallyclosed by a breather or vent plug 112. Body element 96 is also providedwith a passageway 113 through which pass insulated wires connected tothe electric coil 114 and thermistor 115 of an electro-mechanicaltransducer assembly contained in body member 95.

A movable valve element or poppet 110 is contained within the wetchamber 106 and is mounted on the lower end of an operating rod 119which extends through the seal and guide assembly 108. This valveelement 110 has a large diameter head 120 provided with a downwardlyextending peripheral flange 121 which tapers downwardly to a relativelysharp edge. Above head 120, valve element 110 is provided with a shankof small diameter in which is formed a cup 122 in which the lower end ofoperating rod 119 is loosely received. Together with port 100 of bore98, poppet 118 forms a valve assembly which acts on fluid flowing frominlet port 100 to outlet passageway 104 to create a back pressure atport 100. The particular construction shown is preferred for this valvebecause it is self-cleaning and presents a relatively large area to thepressure of fluid at port 100, but it is contemplated that othersuitable constructions may be employed.

The seal and guide assembly 108 includes a circular disk 123 havingcylindrical outer walls. This disk is inserted into that portion of bore105 which cooperates in forming the dry chamber 107 against the shouldertherein which is adjacent the upper end of wet chamber 106. An O-ringseal 124 which is contained within an annular groove in the bore 105adjacent the shoulder engages the cylindrical outer wall of the disk 123and seals it to the bore. The disk 123 is retained against axialmovement in bore 105 by a washer and a snap ring, the latter beingseated in an annular groove in the wall of bore 105. Disk 123 is alsoprovided with a central axial bore through which operating rod 119extends. An O-ring 126 is inserted in a groove adjacent the top of thebore in disk 123 through which the operating rod extends and is heldtherein by the bottom surface of the washer. The rod 119 does notcontact either the disk 123 or the washer and is supported solely byO-ring 126. By these means rod 119 is sealed with guide assembly 100 ina substantially frictionless manner, because the axial motion of rod 119is generally in the nature of not more than two thousandths of an inch,under which conditions O-ring 126 forms an anti-friction bearing, sinceit tends to roll upon the rod as the latter is reciprocated.

The upper end of dry chamber 107 is closed by the previously mentionedflexible boot 109 which is inserted into bore 105 against a shouldertherein. An expansible type coil spring 127 retains boot 109 in bore105, and the boot is provided with a thickened elastic central portionhaving a bore which surrounds and sealingly grips a nonmagnetic brassshaft 128 which carries rod 119.

Body element 95 is cast of a non-magnetic material such as aluminum, andis bored to receive a core 129 in which the coil 114 and thermistor 115of the transducerassembly are housed. Core 129 and an armature disk 130which is positioned above it are preferably formed of material which hashigh magnetic permeability and low hysteresis such as an ingot iron.Core 129 is a cupshaped cylinder having side walls 131 which providemagnetic poles and a hollow center post 132 which also provides magneticpoles. Coil 114 is embedded in an insulating plastic material in thecore 129, while thermistor 115 is embedded in the same plastic materialin a notchlike opening formed in the bottom of the core 129. The outsidediameter of the core 129 is such as to establish a close slidable fitwith bore in body element 95, and the core is provided with a peripheralflange 133 which abuts a shoulder on body element 95. Flange 133 of core129 is clamped to body element by a snap ring in a groove in bodyelement 95.

The electromagnet above described including core 129 and coil 114operates an armature including disk 130. This disk has a hollow hub 135into which a tube 136 of nonmagnetic material is pressed. The armaturedisk 130 extends over the outside magnetic poles formed by the sidewalls 131, and tube 136 extends freely through the center post or poles132 of core 129. The armature disk 130 does not contact body element 95.Shaft 128 fits snugly but axially slidably within tube 136 of thearmature and its upper end is abutted by an adjusting screw 137 which isthreaded into the upper end of tube 136 and which is provided with alocking nut 138. An externally threaded hollow plug 140 covering screw137 and nut 138 is threaded into body member 95. Rotation of core 129and armature disk 130 with respect to each other and body element 95 isprevented by a nonmagnetic pin 141 which extends through disk 130 intoaligned openings in body element 95 and core 129. The opening in thearmature disk 130 through which pin 141 extends is of a diameter largerthan that of pin 141 so that should disk 130 contact the pin duringoperation of the device there will be substantially no frictionalresistance between them. Pin 141 extends through disk 130 to hold itagainst rotation during adjustment of screw 137 and nut 133.

It is to be understood that while the above described pilot valvecomprises a preferred construction, the principles of the invention arenot limited to that specific valve and other specific types ofelectrically operated pilot valves are within the scope of theinvention.

As will be explained, the armature assembly of the transducer iselectromagnetically urged in a direction to close valve 100, 118 and isurged in the opposite direction by fluid pressure acting upon the bottomsurface of the head 12.0 of valve element 118. When this fluid pressureovercomes a predetermined electromagnetic force of the transducer, thevalve will be opened to a position whereat the fluid forces acting uponelement 118 exactly counterbalance the counteracting electromagneticforce. Should the fluid forces acting upon valve element 118 vary ineven the slightest degree, then the opening through the valve 100, 118will be varied to maintain a desired pressure drop between inlet portand outlet bore 104. It has been found during repeated tests and in theactual operation of pilot valve 13 that the valve does not tend to huntwhen the electric current supplied to its coil or the pressureconditions in inlet port 100 are changed, and that the valve respondsquickly even to sudden changes in electric current and/ or pressure.

The force exerted by an electromagnet on an armature spaced from it isinversely proportional to the square of the distance between thearmature and the poles of the magnet for a constant magnetomotive force.For this reason the coil 114 and core 129 of the transducer arepreferably made large in order that there may be a wide air gap betweenthe armature disk 130 and the poles 131 and 132, whereby in that range(0.002 inch) in which the armature moves, the force acting upon thearmature will remain substantially constant for any given magnetomotiveforce produced by the coil 114, and the transducer will deliver asubstantially constant force within its predetermined stroke range inresponse to that magnetomotive force.

Coil 114 will tend to heat up under typical conditions of operation,which normally is accompanied by an in crease in its resistance. Sincethis increase in coil resistance would diminish coil current and therebycause the electromagnetic flux of the coil to decrease, thermistor ispreferably included in series with coil 114 by connection with coil lead142. A resistor R is connected in parallel with thermistor 115 betweenleads 142 and 144. The combination of coil 114, thermistor 115, and resistor R presents a combined resistance between coil leads 143 and 144which varies only a minimal amount 7 with temperature, so that theoverall resistance through which the pilot valve current passes issubstantially constant. The combination of resistance elements will thusbe understood to be equivalent to a temperature constant resistance.

FIGURE 1 shows a preferred electrical circuit 14 whereby the pilot valve13 may be accurately controlled to maintain any flow within a desiredoperating range. It is to be understood that while the circuit shownforms the preferred means for energizing the pilot valve 13, the valvemay be used with any other suitable source of electrical power.

The circuit 14 is designed to operate on conventional 110 Volt, 6% cyclealternating current, is relatively simple and compact, and enables theoperation of the pilot valve to be easily, accurately, and remotelycontrolled over its entire operating range. The circuit includes a powersupply which is shown at the lower left portion of the figure. Thispower supply provides a regulated or constant direct current output atpoints 145 and 146. Power supply leads 147 and 148 are connectable to aconventional source of alternating current not shown.

A resistor R is connected between lead 147 and a junction 15%. A diode Dpermitting current to flow to the right, is connected between junction15% and a second junction 151, while reversely oriented diode Dpermitting current flow to the left but not the right, is connected fromjunction 155 to a junction 152. Condenser C is connected from junction151 to lead 148, and condenser C is connected in series with condenser Cfrom lead 148 to junction 152. Resistor R is connected from junction 151to the plate connection 153 of a voltage regulator tube VR. Junction 152is connected by a lead 154 to the cathode connection 155 of tube VR.

In operation, condensers C and C are charged through diodes D and D onopposite half-cycles of the input current, so that a relatively high,fluctuating potential tends to be established between junctions 151 and152. The voltage regulator tube VR regulates this potential so that alower, substantially constant potential is supplied at points 145 and146, the former being positive with respect to the latter.

Referring now to the preferred control circuit itself, which appears tothe right of the power supply, leads 158 and 159 are connectable to aconventional source of alternating current, as by respective connectionto leads 147 and 14%. Lead 158 is connected to a variable resistor Rwhich has an adjustable tap 160. Tap 160 is connected to one end of theprimary winding of a transformer T, the other end of the primary beingconnected to lead 159.

A variable resistor R having an adjustable tap 161 is connected at oneend to the power supply at 145, tap 161 being connected to a junction162. A variable resistor R having a tap 163 is connected to the powersupply at 1 36 through a lead 164. Tap 163 of resistor R is connected tojunction 162, and a condenser C is connected between junction 162 andlead 164. The secondary winding of the transformer is connected at oneend to lead 1&4 and at the other end to lead 144. The respective taps165i, 161 and 163 of resistors R and R and R are ganged as shown forsimultaneous movement.

Junction 162 is connected through a diode D which permits current flowto the right but not to the left, to a lead 165. Between lead 165 andcoil lead 143 there are connected in parallel a number of variableresistors R R R R and R each resistor having a switch SW SW SW SW and SWrespectively connected in series with it between leads 143 and 165. Thetaps of these resistors are respectively designated 165, 167, 168, 169,and 17%. These taps are preset so that by selectively closing any ofswitches SW SW current will flow from lead 165 to lead 14-3 through aresistor Ti -R of predetermined resistance.

The operation of the pilot valve control circuit 14 may now beexplained. When energized, direct current from the power supply flowsfrom positive connection 145 through resistor R to tap 161, through lead165 to whichever switch ,,SW has been closed, through the resistorconnected in series with that switch to lead 143 and coil 114. From thecoil, the current flows through parallel-connected thermistor andresistor R to lead 144, then through the secondary winding oftransformer T and lead 164 to negative connection 146 of the powersupply. The magnitude of this current may be varied by adjustingvariable resistors R and R The application of an alternating potentialto the primary leads of transformer T induces an alternating potentialin the secondary winding of the transformer which is superimposed on thedirect voltage applied to the coil 114. This alternating voltage isapplied to the circuit through lead 164, condenser C or tap 163depending on the position of the tap along resistor R diode D leads 165and 143, valve coil 114, through thermistor 115 and resistor R andtransformer secondary lead 14 By reason of the superimposition of thealternating potential or voltage established by the transformer on thedirect voltage established by the power supply, the current in coil 1114becomes a modulated or fluctuating direct current which causes the coilflux to fluctuate very rapidly about an average value and therebyminimizes or narrows the range of hysteretic variation of the corematerial. By adding an alternating potential or voltage component to thedirect voltage, the valve response variation due to hysteresis of thecore 129 may be greatly reduced, to as little as plus or minus one-halfof one percent or less. The average direct voltage establishes thesetting of the valve, while the alternating potential or voltage iseffective to minimize the deviation about that setting which is due tothe hysteresis of the core material of the transducer. Because it isdesirable, in connection with the particular pilot valve 13 shown forpurposes of illustration, to use a relatively large alternatingpotential or voltage with a low direct current component of totalcurrent and to use a relatively smaller alternating potential or voltagewith a higher direct current component, the resistors R R and R areganged as shown so that the modulating voltage will be automaticallyreduced as the direct voltage is increased. Thus, as the taps are moveddownwardly on the resistors the direct current is reduced while thealternating component is increased. While this ganging arrangement ispreferred, independently adjustable variable resistors might be used ora single resistor might be substituted in place of the two separateresistors R3 and R4.

From the foregoing, it can be seen that the control circuit 14 iseffective to supply a current to the valve coil 114 such that themagnitude of the flux established by the coil accurately determines thedownward electromagnetic force exerted on the operating rod 119. Thisforce, in turn, determines the pressure drop across valve 100, 118.

In operation, the path of fluid flow through the main flow meteringapparatus 183 is from the inlet port 182 to port 43, then to thecircumferential groove 50, port 44, and from port 44 to passage (theouter end of which forms the high pressure pilot port), leading to ports1% in sleeve 192. From ports 198 the fiuid passes into slot 2% andupwardly in the slot to the adjustable orifice formed by it and slot2'93. From this orifice the fluid flows through a passage leading totank port 134.

The pressure compensator assembly in bore 188 maintains a constantpressure differential between the pressure at port 44 and the pressureat tank port 1&4, or in other words, a constant pressure drop across theadjustable orifice in bore 139, regardless of pressure fluctuations inthe external system. The pressure at port 54 is reflected throughpassageway 6th onto the upper face of piston head 47 and throughdrilling 11 1 and bore 53 to the upper end of shank 48, while thepressure at tank port 184 is reflected into the chamber beneath pistonhead 47 through a bore 210. If, for example, the pressure at port 43rises, the pressure at port 44 will also rise. A larger downward forcewill thereby be exerted on piston 46 in the chamber above the upper faceof piston head 47 and at the upper end of shank 48 through bores 191 and58. This force urges the piston downwardly against the force actingupwardly on it, which is the sum of the nearly constant force of lowrate spring 55 and the force of the fluid beneath piston head 47. Thepiston 46 is moved downwardly by the altered balance of forces acting onit, so that valve 43, 51 is more nearly closed and so that a constantpressure differential is maintained between the pressures at port 44 andoutlet 184. This diiferential is equal to the substantially constantforce of spring 55 divided by the area of piston head 47.

By reason of this constant pressure differential between passageways 98and 104 with which its inlet and outlet respectively communicate, thetrimmer 13 comprises a small secondary orifice capable of veryaccurately controlling the total flow by-passed around fluid motor 11.

,For given coil current, the orifice area presented by valve 100, 118will be constant, as will the pressure drop across it. This being so,the flow through that orifice will be constant for constant coilcurrent. By changing coil current, the pressure drop across valve 100,118 and the area of the orifice presented by it will be changed, so thatthe flow across it will be different. Flow through this orifice willestablish a pressure drop thereacross, and a second drop will beestablished across restricted orifice 99. While changing the coilcurrent will change the relative magnitudes of these drops, their sumwill always equal the pressure differential between passageways 98 and104. For example, when pilot valve 13 is fully open, with no currentapplied to coil 11.14, flow across the valve 100, 118 produces nopressure drop, and the entire pressure differential between bore 98 andbore 104 appears as a drop across restricted orifice 99; if largecurrent is applied to close valve 109, 118 then there is no flow throughthe valve and the entire pressure drop appears across the flange 121.Thus, for any given coil current a definite, fixed trimmer flow can bespecified which, when added to the fixed flow from the main flowmetering assembly, establishes a constant total flow from the flowcontrol assembly.

The system is particularly adapted, for example, to very accuratelymaintain the rate of rotation of a fluid motor at a constant value inspite of variations in the resistance encountered by the motor inperforming work. To this end, the control circuit 14 may be coupled tothe motor 11 through feed-back means such that as motor speed changes,the valve 100, 118 is automatically adusted to permit more or less flowthrough the motor, thereby to bring its speed back to the desired rateof rotation. This may be done, for example, as is shown in the drawing,by driving a fly-ball governor 212 from the motor through gears 213 and214. The governor 212 is physically connected through arm 215 to theganged resistors R R and R in such manner that as the motor 11 slowsdown, greater current is applied to the coil 114 of the trimmer 13 sothat the valve 109, 118, is more nearly closed and less flow is passedaround the motor.

While I have employed a fly-ball governor 212 to illustrate one meansfor carrying out a feed-back function, it is to be understood that thescope of the invention, in this respect, is intended to include anydevice, whether electrical, hydraulic or mechanical, which will carryout a feed-back function equivalent to that described. Those skilled inthe art will understand that the principles of the invention are notlimited to use with the particular main flow metering assembly, pressurecompensator pilot valve, or circuitry shown, but also include othervariations or modifications falling within the scope and spirit of theclaims as follows.

I claim:

1. Apparatus for controlling the rate of flow of a fluid, said apparatuscomprising, (a) main flow metering means, said main flow metering meanscomprising, a body having an inlet port, an outlet port, and anadjustable member forming an orifice with said body between said inletport and said outlet port, said member being adjustably positionablewith respect to said body to vary the area of said orifice, (b) trimmerflow metering means including a movable valve element cooperable with acontrol port, an inlet and an outlet, one of which includes a restrictedorifice, an electromechanical transducer for supplying a force urgingsaid valve element relative to said control port the magnitude of whichforce corresponds to an electrical signal applied to said transducer,(c) pressure regulator means for maintaining a constant pressuredifferential between fluid pressures at the inlet and outlet ports ofsaid main flow metering means and between fluid pressures at the inletand outlet of said trimmer flow metering means, (d) means connecting theoutlet port of said main flow metering means with the outlet of saidtrimmer flow metering means, and (e) means responsive to the rate offlow of fluid at a point served by said apparatus for controlling theelectrical signal applied to said transducer, the signal applied to saidtransducer determining the flow through said trimmer flow metering meansto said outlet, the position of said adjustable member with respect tosaid body determining the flow through said main flow metering means tosaid outlet port.

2. Apparatus for controlling the speed of a fluid motor, said apparatuscomprising, (a) main flow metering means, said main flow metering meanscomprising, a body having an inlet port, an outlet port, and anadjustable member forming an orifice with said body for controlling theflow from said inlet port to said outlet port, said member beingadjustably positionable with respect to said body to vary the area ofsaid orifice, (b) pressure compensator means for maintaining a constantdifferential between fluid pressures at said inlet and outlet ports fora given position of said member with respect to said body, (0) trimmerflow metering means including a movable valve element cooperable with acontrol port, an inlet and an outlet, an electromechanical transducerfor supplying a force urging said valve element relative to said controlport the magnitude of which force is controlled by an electrical currentapplied to said transducer, ((1) fluid passageways including, apassageway communicating between the inlet port of said main flowmetering means and the inlet of said trimmer flow metering means, and apas sageway communicating between the outlet port of said main flowmetering means and the outlet of said trimmer flow metering means, oneof said passageways including a restricted orifice, and (e) meansresponsive to the speed of a fluid motor served by both of said meteringmeans for controlling the electrical current applied to said transducer.

3. Flow control apparatus comprising, (a) main orifice means, said mainorifice means comprising a body having an inlet port and an outlet portand an adjustable member forming an orifice with said body between saidinlet port and said outlet port, said adjustable member being adjustablypositionable with respect to said body to vary the area of said orifice,(b) pressure compensator means for maintaining a differential betweenfluid pressures at said inlet and outlet ports which is substantiallyconstant for any given position of said adjustable member with respectto said body, (0) trimmer valve means having an inlet and an outlet, amovable valve element cooperable with a control port between said inletand outlet for establishing a pressure drop, an electromechanicaltransducer for actuating said valve element relative to said controlport to control the magnitude of said pressure drop in accordance withan electric signal applied to said transducer, said transducer supplyinga force for actuat ing said valve element relative to said control portwhich force is substantially constant for a given electric signalapplied to said transducer over the range of movement of said valveelement relative to said control port, and (d) fluid passagewaysincluding a passageway communicating between the inlet port of said mainorifice means and the inlet of said trimmer valve means and a passagewaycommunicating between the outlet port of said main orifice means and theoutlet of said trimmer valve means, one of said passageways including afixed flow restrictor, the position of said adjustable member withrespect to said body determining the flow through said main orificemeans and the electrical signal applied to said transducer determiningthe flow through said trimmer valve means.

4. Flow control apparatus comprising, (a) main orifice means, said mainorifice means comprising a body having an inlet port and an outlet portand an adjustable member forming an orifice with said body between saidinlet port and said outlet port, said member being adjustablypositionable with respect to said body to vary the area of said orifice,(b) trimmer valve means having an inlet and an outlet, a movable valveelement cooperable with a control port between said inlet and outlet forestablishing a pressure drop, an electromechanical transducer foractuating said valve element relative to said control port to controlthe magnitude of said pressure drop in accordance with an electricsignal applied to said transducer, said transducer supplying a force foractuating said valve element relative to said control port which isconstant over the range of movement of said valve element with respectto said control port for any given signal applied to said transducer,(0) a fluid passageway communicating between the inlet of said trimmervalve means and the inlet port of said main orifice means, a fluidpassageway communicating between the outlet of said trimmer valve meansand the outlet port of said main orifice means, one of said fluidpassageways including a fixed flow restrictor, and (d) pressurecompensator means for maintaining a constant pressure differentialbetween the pressures of fluid at the inlet and outlet ports of saidmain orifice means,

5. Flow control apparatus comprising, (a) main orifice means, said mainorifice means comprising a body having an inlet port and an outlet portand an adjustable member forming an orifice with said body between saidinlet port and said outlet port, said member being adjustablypositionable with respect to said body to vary the area of said orifice,(b) trimmer orifice means having an inlet and an outlet, a movable valveelement cooperable with a control port between said inlet and outlet forestablishing a pressure drop, an electromagnetic transducer foractuating said valve element relative to said control port to controlthe magnitude of said pressure drop in response to a current applied tosaid transducer, said transducer supplying a force urging said movablevalve element toward said control port which force is substantiallyconstant for any given current over the range of movability of saidvalve element relative to said control port, a fixed flow restrictor inseries with said control port between said inlet and outlet, (c)pressure regulator means for maintaining a constant pressuredifferential between fluid pressures at the inlet and outlet ports ofsaid main orifice means and between fluid pressures at the inlet andoutlet of said trimmer orifice means, and ((1) means connecting theoutlet port of said main orifice means and the outlet of said trimmerorifice means.

References Cited by the Examiner UNITED STATES PATENTS 2,031,478 2/1936Gray 137-505.11 2,879,643 3/1959 Stroh 137-117 XR 2,986,161 5/1961Renick 137501 XR 3,105,671 10/1963 Teitelbaurn et al 2513O 3,115,89212/1963 Brewer 137501 M. CARY NELSON, Primary Examiner.

MARTIN P. SCHWADRON, Examiner,

1. APPARATUS FOR CONTROLLING THE RATE OF FLOW OF A FLUID, SAID APPARATUSCOMPRISING, (A) MAIN FLOW METERING MEANS, SAID MAIN FLOW METERING MEANSCOMPRISING, A BODY HAVING AN INLET PORT, AN OUTLET PORT, AND ANADJUSTABLE MEMBER FORMING AN ORIFICE WITH SAID BODY BETWEEN SAID INLETPORT AND SAID OUTLET PORT, SAID MEMBER BEING ADJUSTABLY POSITIONABLEWITH RESPECT TO SAID BODY TO VARY THE AREA OF SAID ORIFICE, (B) TRIMMERFLOW METERING MEANS INCLUDING A MOVABLE VALVE ELEMENT COOPERABLE WITH ACONTROL PORT, AN INLET AND AN OUTLEWT, ONE OF WHICH INCLUDES ARESTRICTED ORIFICE, AN ELECTROMECHANICAL TRANSDUCER FOR SUPPLYING AFORCE URGING SAID VALVE ELEMENT RELATIVE TO SAID CONTROL PORT THEMAGNITUDE OF WHICH FORCE CORRESPONDS TO AN ELECTRICAL SIGNAL APPLIED TOSAID TRANSDUCER, (C) PRESSURE REGULATOR MEANS FOR MAINTAINING A CONSTANTPRESSURE DIFFERENTIAL BETWEEN FLUID PRESSURES AT THE INLET AND OULTETPORTS OF SAID MAIN FLOW METERING MEANS AND BETWEEN FLUID PRESSURES ATTHE INLET AND OUTLET OF SAID TRIMMER FLOW METERING MEANS, (D) MEANSCONNECTING THE OUTLER PORT OF SAID MAIN FLOW METERING MEANS WITH THEOUTLET OF SAID TRIMMER FLOW METERING MEANS, AND (E) MEANS RESPONSIVE TOTHE RATE